I urge most folks to use the utility grid with their RE system. More than 40 U.S. states have some form of net metering available. This means that a large majority of U.S. utility customers can “bank” any surplus energy their PV system produces with their local utility, and use the credit to pay for future utility electricity usage.
Almost all U.S. homes have grid service available, and it’s surprisingly reliable. Some locations may be less reliable, and it makes sense to find out how often your region has outages, and how long they typically last. If having completely uninterrupted electricity is important to you, a battery-based grid-tied system could be the best of both worlds—renewable electricity with utility outage protection. These systems provide electricity (usually for dedicated, not whole-house, loads) when the grid is down.
The most common grid-tied systems do not use batteries, and therefore do not have outage protection—their one disadvantage. Their advantages include lower cost, less complexity, lower maintenance, lower environmental impact, higher operational efficiency, and a longer overall system life, since there are no batteries to replace and fewer components.
Your motivations and goals are key in coming up with your own answer. It doesn’t need to make sense to anyone else if you want to be off-grid. But it is important to be realistic about what can be done and what it will cost—both in dollars, and in your time and attention. Additionally, there are some situations that make off-grid living either the only possible option or the most appropriate.
If you have property miles from the grid, or in a location that has no grid, your only affordable option may be to set up an independent system. If extending the utility grid to your property is possible, find out how much it will cost, and what the ongoing cost will be. Then you can make a sensible comparison to base your decision on. While $20,000 in line-extension costs may seem high, if you are looking to power a large home that has many loads, spending that money may be the best option. Be realistic about the burden (financial and otherwise) of living off-grid! On the other end of the scale, if it’s going to cost you a quarter of a million dollars to extend the grid, an off-grid system may be very economical and sensible. (See “Methods” in this issue for more on the economics.)
There are situations where utility policies make connection costly or difficult. While many utilities encourage RE systems, others seem to throw up roadblocks to easy interconnection. Some utilities have high monthly base charges. Others require expensive equipment that is not necessary to safe interconnection. And others have burdensome paperwork and/or insurance requirements. Talking with your local utility, installers, and other RE users will help you understand the full cost and difficulty. Then you can make a sensible decision.
The first major task in off-grid system design is load analysis. Without accurate measurements or estimates of energy use, it’s impossible to design a system that will satisfy the need in the most economical way. Electricity consumption is measured in kilowatt-hours (kWh), and an accurate daily or monthly number is needed to start your system design.
If you currently live on-grid, you can start with your utility bill, which tells you how many kWh were used during the last billing period, and often summarizes the last year or more. Even better would be to have a year’s worth of bills—which should be available from your utility. This will give you a baseline for your current energy lifestyle. Then you need to estimate how much energy your off-grid lifestyle will use. To be most cost-effective, you need to identify energy-efficiency and conservation measures you can implement, and you’ll likely need to shift some loads from electricity to other energy sources.